These pumps in general include a magnetic circuit for the creation of a field passing through the channel for pumping the metal and a turn of refractory material inside which is liquid metal in electrical contact with the metal contained in the rising pumping channel, at the level of the zone subjected to the magnetic field.
Such pumps are described in French Pat. No. 2,164,493, and are illustrated in FIG. 1 of the present application.
A pump of this type comprises a rising channel for pumping of the liquid metal 1 which passes through the gap 2 of a first electromagnetic circuit in the form of a yoke 3. This yoke is associated with a coil 4 wound round one side of it, which is fed with alternating current so as to create in the section of liquid metal located in the gap 2 a horizontal magnetic field.
The pump includes, in addition a second magnetic circuit in the form of a frame 5, a feed coil 6 wound round one side of the frame 5 and a conductive turn 7 of rectangular section surrounding another side of the frame 5.
The coil 6 is fed with alternating current so as to induce an alternating current in the loop 7. This loop 7 consists of liquid metal contained in a refractory envelope 8. This envelope 8 is connected to the channel 1 by two mouthpieces 9 and 9' each having an opening which puts the interior of the envelope 8 into communication with the interior of the channel 1, with the result that the metal can flow between the envelope 8 and the channel 1. The section of metal located between the two mouthpieces 9 and 9' is traversed by the alternating current generated in the loop 7.
The loop 7 is arranged so that the current flowing between the mouthpieces 9 and 9' is at right angles to the magnetic field created in the gap 2 and to the axis of the channel 1.
In order that the vertical electromagnetic force which is then created in the section of metal located between the mouthpieces 9 and 9' may always remain rising, it is necessary to see to it that the current and the magnetic field are approximately in phase.
Even if such pumps give satisfaction it is, however, found that with time the particles which are not conductive of electricity and which are carried along by the liquid metal have a tendency to be deposited in the loop 7 through which is generated the current which passes into the channel of liquid metal.
In the pumps which have just been described the loop 7 is consequently difficult to clean. An attempt to overcome this disadvantage is disclosed in a French application (published under Ser. No. 2,360,206). It refers to a variant of the pumps described above, in which the loop is rectilinear and opens into the metal bath through which the induced currents are closed.
Such pumps are of interest with respect to the cleaning of the loop, but the performance obtained is interior to that of the machines which are the object of French Pat. No. 2,164,493. This is due in particular to the fact that the loop, being rectilinear, is coupled more loosely to the arm of the frame 5 than in French Pat. No. 2,164,493. Again, the path of the loop being much longer than in the pumps of the latter patent, the loop opposes a high resistance to the induced current.